Serial optical communication links experience many different kinds of errors and failure behaviors. At one extreme are the occasional single bit errors. These errors cause a single bit in the bit stream to be flipped or complemented and are caused by random noise. When these errors happen during an idle sequence, no recovery action is required. When they happen within an information frame, various recovery actions are taken depending on what part of the frame is corrupted. At the other extreme are link failures that lead to a total loss of communication. These can be caused by anything from a critical component failure, to losing power at one end of the link, to a physical disconnection of the optical fiber transmission medium. Very often, especially when an optical connector somewhere in the operating link is physically disconnected, the link failure condition is preceded by an increasing bit error rate. In some cases a link failure condition is detected followed by a reestablishment of the link followed by a link failure condition multiple times as the optical connector is being slowly disconnected.
Serial optical communication links are usually driven by adapters that have a dedicated processor. In these implementations, the processor is interrupted as each link error and failure event is recognized by the inbound decoder state machines. Even when the link error rates are very high, as when an optical connector is being disconnected, the dedicated processor can keep up with the error events since it has nothing else to do during these high error rate periods.